What should I do about a debt that arose from embezzling a sum of money from an employer who has passed away, knowing that I am unable to repay it due to financial and health reasons, and long distance?

Your regret is proof of the sincerity of your repentance. Therefore, seek forgiveness from Allah and resolve to fulfill the right of the man's heirs whenever you are able. It is hoped that Allah will assist you in this due to your sincere intention. If you are unable to repay it before your death, it is hoped that Allah will repay it on your behalf, as supported by the Hadith: "Whoever takes people's money with the intention of repaying it, Allah will repay it on his behalf; and whoever takes it with the intention of destroying it, Allah will destroy him." If you find a way to repay, return the entire amount. You are not required to inform them of the embezzlement; rather, it is sufficient to pay it to them as a right that their deceased relative had over you.